[erlang-questions] Experience with much memory

[Mikael Pettersson]

On Sat, Sep 28, 2019 at 4:03 PM <buday.gergely@REDACTED> wrote:
>
> Hi there,
>
> are there experience reports on using Erlang/Elixir on systems with 200 GB of memory and more?
>
> If you have a first-hand account on that, please share it with me.

The Erlang/OTP VM handles that and more without much trouble.  We have
been running Erlang on servers with multi-TB RAM for many years now.
There are a few things to look out for:

- Use a recent (say OTP-19 or above) version of the VM, older ones had
integer truncation bugs that could lead to wrong results or
segmentation faults when dealing with very large terms.
- Disable transparent hugepages in the Linux kernel, that's been known
to cause huge unpredictable pauses or even kernel crashes.  (May or
may now have been fixed now, but was certainly true in RHEL/CentOS 6.)
- Page fragmentation is an issue, also causing occasional pauses when
the Linux kernel goes busy.  Watch buddyinfo, drop caches sometimes,
and _maybe_ even compact memory.  However, dropping caches hurts file
system performance so don't do that unnecessarily.
- Increase max_map_count.  At TB sizes the VM can reach the default
limit and the failures are _not_ easy to debug.